The long-term goals of this project are to further our understanding of how peripheral auditory processing affects perception, and to investigate the extent to which the physiological changes associated with cochlear damage can account for the perceptual difficulties faced by people with hearing loss. The first aim is to investigate behavioral measures of cochlear function in humans. Behavioral methods of estimating basilar-membrane (BM) compression will be compared in terms of accuracy and efficiency in normal-hearing and hearing-impaired listeners. These methods will then be used to assess the effects of broadband noise on estimated BM compression, to test the hypothesis that broadband noise linearizes the response to tones through the effects of suppression. Current behavioral measures of BM compression are not efficient enough for clinical applications. New behavioral measures, suitable for potential clinical use, will therefore be developed. Work will also continue towards providing a comprehensive description of normal and impaired human cochlear filtering over a wide range of frequencies and levels. The second aim is to investigate temporal resolution in humans using behavioral measures that, unlike many current measures, are not confounded by the influence of BM compression. This will allow us to test for effects of ageing on temporal processing, independent of the effects of cochlear nonlinearity. It will also allow us to test the hypothesis that listeners who exhibit abnormally poor word recognition for a given hearing loss suffer from deficits in temporal processing. The third aim is to use the new measures of BM compression and temporal resolution to predict normal-hearing and hearing-impaired listeners' speech reception thresholds in complex backgrounds, such as fluctuating noise and single-talker interference. This will test the hypothesis that deficits in speech reception by hearing-impaired listeners in complex acoustic environments is influenced both by deficits in cochlear processing and, in some cases, by deficits in higher-level temporal processing. A better understanding of normal cochlear function in humans has many applications, including biologically based front-end processors for speech recognition and improved preprocessors for cochlear implants. Better understanding of the deficits suffered by hearing-impaired listeners should lead to more accurate diagnoses on an individual basis, which in turn should lead to improved hearing aid algorithms and fitting procedures.